Remove presales Zendesk code

### Quick summary

We have the Zendesk presales widget disabled in Network Admin settings, but it appears it still showing based on 9257010-zd-a8c for example as they interacted with the widget previously and were able to see the agent's name, which is not shown in Help Center. I suspect this is due to some form of caching and I am unsure if we can prevent it, but removing the widget code more completely is likely worthwhile to start since we do not have short-term plans to re-enable it.

p1736350628818979-slack-CB0B2G43X

### Steps to reproduce

Unable to reproduce as I believe caching is involved if they viewed/opened the widget before

### What you expected to happen

Users to not be able to see the native Zendesk widget

### What actually happened

somehow the user saw the agent's name and a response was not emailed, indicating the native widget was loaded.

### Impact

Some (< 50%)

### Available workarounds?

There is no user impact

### If the above answer is "Yes...", outline the workaround.

_No response_

### Platform (Simple and/or Atomic)

_No response_

### Logs or notes

_No response_